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T. Bellezze, G. Giuliani, G. Roventi, “Study of stainless steels corrosion in a strong acid mixture. Part 1: cyclic potentiodynamic polarization curves examined by means of an analytical method”, Corrosion Science, 130 (January), 2018, 113-125
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Abstract:
The corrosion resistance of AISI 316L, AISI 904L, Sanicro 28, SAF 2205, SAF 2507 and SAF 2707 was studied in an acid mixture containing tartaric acid saturated solution, H2SO4 and HCl, as a function of temperature (22–60 °C) and alloys composition. The stainless steels were examined through anodic polarization curves; an analytical method is proposed to obtain the characteristic parameters from these curves. The results indicate that Cr and Mo play the most important role on the active-passive transition of the tested alloys. AISI 904L, Sanicro 28 and SAF 2707 showed the best anodic characteristics among the examined stainless steels.
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T. Bellezze, G. Giuliani, A. Viceré, G. Roventi, “Study of stainless steels corrosion in a strong acid mixture. Part 2: anodic selective dissolution, weight loss and electrochemical impedance spectroscopy tests”, Corrosion Science, 130 (January), 2018, 12-21
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Abstract:
The corrosion resistance of austenitic stainless steels AISI 316L, AISI 904L and Sanicro 28 and duplex stainless steels SAF 2205, SAF 2507 and SAF 2707, was studied at 40 and 60 °C in a strong acid mixture containing tartaric acid saturated solution, H2SO4 and HCl. Anodic selective dissolution, weight loss and electrochemical impedance tests were performed. The results show that all stainless steels corrode actively and the micro-galvanic coupling, present on duplex stainless steels and 316L, determines severe selective corrosion and impairs their tendency to passivate. 904L and Sanicro 28 showed this tendency and the lowest corrosion rates.
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T. Bellezze, D. Timofeeva, G. Giuliani, G. Roventi, “Effect of soluble inhibitors on the corrosion behaviour of galvanized steel in fresh concrete”, Cement and Concrete Research, 107 (May), 2018, 1-10
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Abstract:
The effect of some soluble inhibitors on the passivation time of galvanized steel reinforcements in fresh concrete was studied in order to reduce H2 evolution associated with the active corrosion. The investigation was performed by means of corrosion potential monitoring, scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction analysis. The obtained results indicate that the passivation of galvanized steel in concrete containing chromates occurs in three steps with different mechanisms and that dissolved oxygen is necessary for the beginning of passivation process. Among the inhibitors studied as alternative to Cr VI, nitrite seem the most promising one, even if it is less effective than chromate. Diethanolamine and molybdate ions do not have significant effect on the passivation time of galvanized steel in fresh concrete.
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F. Tittarelli, A. Mobili, C. Giosuè, A. Belli, T. Bellezze, “Corrosion behaviour of bare and galvanized steel in geopolymer and Ordinary Portland Cement based mortars with the same strength class exposed to chlorides”,Corrosion Science,134 (April), 2018, 64-77
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Abstract:
The corrosion behaviour of bare and galvanized steel reinforcements in geopolymeric and cementitious mortars, at three strength classes, has been investigated throughout the curing period and exposure to wet-dry cycles in 3.5% NaCl solution. During the curing, the high alkalinity of geopolymers prolongs the active state of both bare and galvanized steel. During the chloride exposure, fly ash geopolymers give the highest protection to reinforcements. The higher alkalinity of geopolymers compared to cement mortars seems to decrease the minimum free chloride threshold necessary to induce corrosion for galvanized steel, but it increases that for bare steel.
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M. Cabibbo, E. Santecchia, P. Mengucci, T. Bellezze, A. Viceré, “The role of cryogenic dipping prior to ECAP in the microstructure, secondary-phase precipitation, mechanical properties and corrosion resistance of AA6012 (Al-Mg-Si-Pb)”, Materials Science and Engineering A, 716 (February), 2018, 107-119
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Abstract:
Literature on ECAP generally deals with room temperature or high-temperature deformation regimes. Very few data on low-temperature SPD processes have been published. This study presents some experimental results on the effect of cryogenic treatment prior to ECAP-BC on microstructure modification, mechanical response, and corrosion behaviour of an AA6012 Al-Mg-Si-Pb alloy. This type of Pb-bearing AA6000-series alloy, is produced and used for its marked post-extrusion machinability. The mechanical properties were inferred by nanoindentation to measure hardness, H, and local elastic modulus, Er. These data were presented in form of maps to account for the whole H and Er evolution with cumulative strain. The experimental results showed significant microstructure differences between the cryogenic treated ECAP condition and the conventional ECAP at room temperature. These differences were also correlated with electron microscopy inspections, XRD. Finally, the cryogenic treatment prior ECAP also affected the alloy corrosion behaviour.
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M. Pea, G. Barucca, A. Notargiacomo, L. Di Gaspare and V. Mussi, “Zn nanoparticle formation in FIB irradiated single crystal ZnO”, Applied Surface Science, 433 (March), 2018, 899–903
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Abstract:
We report on the formation of Zn nanoparticles induced by Ga+ focused ion beam on single crystal ZnO. The irradiated material has been studied as a function of the ion dose by means of atomic force microscopy, scanning electron microscopy, Raman spectroscopy and transmission electron microscopy, evidencing the presence of Zn nanoparticles with size of the order of 5-30 nm. The nanoparticles are found to be embedded in a shallow amorphous ZnO matrix few tens of nanometers thick. Results reveal that ion beam induced Zn clustering occurs producing crystalline particles with the same hexagonal lattice and orientation of the substrate, and could explain the alteration of optical and electrical properties found for FIB fabricated and processed ZnO based devices.
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F. Naspi, M. Arnesano, L. Zampetti, F. Stazi, G.M. Revel, M. D’Orazio, “Experimental study on occupants interaction with windows and lights in Mediterranean offices during the non-heating season”, Building and Environment, 127, 2018, 221-238
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Abstract:
The modelling of human behaviour is an important challenge for the building sector, as the actions of users have significant impacts on both energy consumption and comfort assessment. In the search for a comprehensive understanding of the behaviour of occupants, many researchers have directed their efforts towards determining typical patterns and developing models to predict human-building interactions. This study investigates the behaviour of building users during the summer season in offices in Mediterranean climate. Studies focusing on this area are still lacking, despite their importance for cooling loads. A survey is conducted using a dedicated sensor network to monitor environmental variables, and to determine the presence of people and their interactions with windows and lights in three offices. The driving factors for the actions of users are assessed and behavioural models are proposed. The results indicate that interactions with windows and lights are driven by both timerelated events and environmental factors, confirming previous findings. A comparison of the proposed models with others developed for different climate zones suggests that interactions with windows are affected by the geographic area, while light switching behaviour seems to be very similar for the different case studies. A simplified approach for the consideration of different user-device interactions is also proposed. This novel method, developed to evaluate the interactivity between users and building systems, is based on a coefficient of interactivity, CI. Both the behavioural models and the simplified approach could be introduced into future simulations to improve predictions of energy use in buildings.
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F. Stazi, F. Tittarelli, F. Saltarelli, G.Chiappini, A.Morini, G.Cerri, S.Lenci, “Carbon nanofibers in polyurethane foams: Experimental evaluation of thermo-hygrometric and mechanical performance”, Polymer testing, 67, 2018, 234-245
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Abstract:
Polymer nanocomposites synergistically combine the good thermal properties of the hosting polymer matrix with the high mechanical performance of the fillers, providing a new class of materials with superior properties. The present study aims to evaluate in a multidisciplinary way the enhancement in mechanical and thermalhygrometric properties of low and medium density nanophased polyurethane (PUR) foams with either randomly oriented or aligned nanofibers as compared to the neat ones. To this aim, 1% weight of carbon nanofibers (CNFs) were homogeneously dispersed into polyol of PUR foam by an ultrasonic cavitation method. In parallel, a small amount of CNFs was functionalized in advance by a coprecipitation method so as to align them into the polymer matrix through an external low intensity magnetic field. SEM analyses were used to compare the microstructure of the neat and nanophased samples. Results have shown that the addition of carbon nanofibers in the foams products a closer structure with a more uniform size and shape. Moreover, functionalized CNFs play a significant role in regulating cells shape as well as strengthening cells walls. Mechanical test results also demonstrated that CNFs increase both strength and stiffness of the samples. The alignment of carbon nanofibers within medium density nanophased foams determines the highest mechanical properties. However, the more noticeable improvement in samples performance occurred in low densitynanophased foams. Finally, carbon nanoparticles decrease the thermal conductivity and increase the resistance against water adsorption.
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F. Vita, F. C. Adamo, O. Francescangeli, “Polar order in bent-core nematics: An overview”, Journal of Molecular Liquids, 2018, in press. DOI: 10.1016/j.molliq.2018.02.084
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Abstract:
The possible existence of a ferroelectric nematic phase has been challenging liquid crystal scientists since it was first envisaged about 30. years ago. At present, an undisputable proof of proper ferroelectricity in low-molecular weight thermotropicnematics is still missing. However, over the last decade several groups have reported the observation of a ferroelectric-like switching behavior in the nematic phase of a number of bent-core mesogens. This effect is generally ascribed to polar clusters of molecules, known as cybotactic groups, permeating the nematic phase. In the unperturbed state the cluster dipoles are randomly oriented, so that the phase is macroscopically uniaxial and apolar; however, an external field exceeding a threshold is able to align the cluster dipoles, inducing the transition to a switchable polar and biaxial state. Even though this behavior clearly differs from that expected in a proper ferroelectric liquid crystal, it still deserves considerable interest for its potential implications from both a fundamental and a technological point of view. Here we review the studies devoted to this extraordinary effect, both experiments and simulations, and discuss the open questions that still remain unanswered.
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Spinelli, M., Eusebi, A.L., Vasilaki, V., Katsou, E., Frison, N., Cingolani, D., Fatone, F. “Critical analyses of nitrous oxide emissions in a full scale activated sludge system treating low carbon-to-nitrogen ratio wastewater”, Journal of Cleaner Production, Volume 190, 20 July 2018, Pages 517-524
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Abstract:
A critical analysis of nitrous oxide emissions in a full-scale modified LudzackEttinger plant treating municipal wastewater with low carbon to nitrogen ratio is presented. The results of N2O emissions were processed by coupling classical (liquid chemical/physical characterization) and new data analytics techniques (online gaseous emissions and statistical analysis). Correlation between the operational parameters of the plant and long-term online monitored nitrous oxide emissions was conducted. The analysis considered the effect of off-gas sampling methods, the variability of feeding characteristics and the main liquid process variables as the principle parameters that may affect nitrous oxide emissions. In order to detect and assess the causal relationships between online monitored system variables and nitrous oxide emissions, statistical and event-based sensitivity analysis was adopted to identify causal relationships between the variables of the system. Observations revealed that lower ratio between carbon and nitrogen (COD:N) resulted in higher N2O emissions. The average nitrous oxide emission factors changed from 0.0089 gN2O/kgTNin to 0.051 gN2O/kgTNin, that corresponded to denitrification limited by organic carbon availability. The nitrous oxide dynamics were not significantly influenced by dissolved oxygen variations (within the range of 1.5–2 mg/L). However daily peaks of nitrous oxide emissions occurred when aeration flow-rate resulting was higher and stripped more nitrous oxide from liquid
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Frison, N., Malamis, S., Katsou, E., Bolzonella, D., Fatone, F. Enhanced retention of deammonification microorganisms for the treatment of psycrophilic anaerobic digestate, Chemical Engineering Journal ,Volume 344, 15 July 2018, Pages 633-639
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Abstract:
This study focused on the treatment of psychrophilic anaerobic digestate from pig slurry digestion through a single-stage Sequencing Batch Reactor (SBR) accomplishing the autotrophic nitrogen removal (ANR). In period 1, the combination of the high sludge retention time (>50 days) and the presence of significant concentrations of biodegradable organic carbon favoured the uncontrolled growth of the denitrifying bacteria (HDB) and the nitrite oxidizing bacteria (NOB), affecting negatively the deammonification (DAM) activity from 14 to 15 mgN/gMLVSS·h to only 2.2 mgN/gMLVSS·h. In Period 2, the sieving of the suspended biomass at 125 µm was evaluated to enhance the retention time of DAM microrganisms in granular sludge into the SBR. This strategy allowed the recovery of 60% of the initial specific deammonification activity (sDAA) and to promote the wash-out of the NOB, obtaining a nitrogen removal efficiency of 81%. This method was never applied to increase the robustness and reliability of ANR during the treatment of livestock streams, so it could be considered after optimization as a potential option to increase the sustainability of smaller and local farms.
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Bolzonella, D., Fatone, F., Gottardo, M., Frison, N. Nutrients recovery from anaerobic digestate of agro-waste: Techno-economic assessment of full scale applications. Journal of Environmental Management Volume 216, 15 June 2018, Pages 111-119
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Abstract:
The sustainable production of fertilizers, especially those based on phosphorus, will be one of the challenges of this century. Organic wastes produced by the agriculture, urban and industrial sectors are rich in nutrients which can be conveniently recovered and used as fertilizers. In this study five full scale systems for the recovery of nutrients from anaerobic digestate produced in farm-scale plants were studied. Monitored technologies were: drying with acidic recovery, stripping with acidic recovery and membrane separation. Results showed good performances in terms of nutrients recovery with average yields always over 50% for both nitrogen and phosphorus. The techno-economic assessment showed how the specificity of the monitored systems played a major role: in particular, membranes were able to produce a stream of virtually pure water (up to 50% of the treated digestate) reducing the digestate volume, while drying, because of the limitation on recoverable heat, could treat only a limited portion (lower than 50%) of produced digestate while stripping suffered some problems because of the presence of suspended solids in the liquid fraction treated. Specific capital and operational costs for the three systems were comparable ranging between 5.40 and 6.97 € per m3 of digestate treated and followed the order stripping > drying > membranes. Costs determined in this study were similar to those observed in other European experiences reported in literature.
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Crutchik, D., Frison, N., Eusebi, A.L., Fatone, F. Biorefinery of cellulosic primary sludge towards targeted Short Chain Fatty Acids, phosphorus and methane recovery Water Research Volume 136, 1 June 2018, Pages 112-119
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Abstract:
Cellulose from used toilet paper is a major untapped resource embedded in municipal wastewater which recovery and valorization to valuable products can be optimized. Cellulosic primary sludge (CPS) can be separated by upstream dynamic sieving and anaerobically digested to recover methane as much as 4.02 m3/capita·year. On the other hand, optimal acidogenic fermenting conditions of CPS allows the production of targeted short-chain fatty acids (SCFAs) as much as 2.92 kg COD/capita·year. Here propionate content can be more than 30% and can optimize the enhanced biological phosphorus removal (EBPR) processes or the higher valuable co-polymer of polyhydroxyalkanoates (PHAs). In this work, first a full set of batch assays were used at three different temperatures (37, 55 and 70 °C) and three different initial pH (8, 9 and 10) to identify the best conditions for optimizing both the total SCFAs and propionate content from CPS fermentation. Then, the optimal conditions were applied in long term to a Sequencing Batch Fermentation Reactor where the highest propionate production (100–120 mg COD/g TVSfed·d) was obtained at 37 °C and adjusting the feeding pH at 8. This was attributed to the higher hydrolysis efficiency of the cellulosic materials (up to 44%), which increased the selective growth of Propionibacteriumacidopropionici in the fermentation broth up to 34%. At the same time, around 88% of the phosphorus released during the acidogenic fermentation was recovered as much as 0.15 kg of struvite per capita·year. Finally, the potential market value was preliminary estimated for the recovered materials that can triple over the conventional scenario of biogas recovery in existing municipal wastewater treatment plants.
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Cingolani, D., Fatone, F., Frison, N., Spinelli, M., Eusebi, A.L. Pilot-scale multi-stage reverse osmosis (DT-RO) for water recovery from landfill leachate. Waste ManagementVolume 76, June 2018, Pages 566-574
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Abstract:
Recovery of high quality water from municipal landfill leachate was studied by three-stage disc tube reverse osmosis optimized in pilot-scale. Following UF-membrane-assisted activated sludge plant, overall 46.5 tons of leachate were post-treated in real environment and analyzed for conventional contaminants and hazardous compounds (e.g. heavy metals, boron, selenium) throughout operation of membrane system. Operating pressure ranged from 21 to 76 bar, while permeate flux varied in the range 7.1–32.5 L m−2 h−1. Rejection factors of specific ions were related to the pressure and global removals were assessed for each stage (e.g. E%COD = 92.4–99.2%, E%NH4 = 46.2–95.8%, E%NOx = 84.8–97.9%; E%TDS = 88–95.5%). Boron removal was assessed in the range 34–48%, so as to require the third stage to reach standard for discharge or reuse. Two stages were sufficient to reach water recovery higher than 91%. Long-term operation and mathematical modeling demonstrated how the Δπ/ΔP ratio can support the decisions for membrane cleaning and predictive maintenance: permeability decline was associated to the ratio increase from 0.72 to 0.73 to 1.13–1.21.
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Wang, K.M., Cingolani, D., Eusebi, A.L., Soares, A., Jefferson, B., McAdam, E.J. Identification of gas sparging regimes for granular anaerobic membrane bioreactor to enable energy neutral municipal wastewater treatment. Journal of Membrane Science Volume 555, 1 June 2018, Pages 125-133
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Abstract:
In this study, conventional and novel gas sparging regimes have been evaluated for a municipal wastewater granular anaerobic MBR to identify how best to achieve high sustainable fluxes whilst simultaneously conserving energy demand. Using continuous gas sparging in combination with continuous filtration, flux was strongly dependent upon shear rate, which imposed a considerable energy demand. Intermittent gas spargingwas subsequently evaluated to reduce energy demand whilst delivering an analogous shear rate. For a flux of 5 L m−2 h−1, a fouling rate below 1 mbar h−1 was sustained with low gas sparging frequency and gas sparging rates. However, to sustain low fouling rates for fluxes above 10 L m−2 h−1, a gas sparging frequency of 50% (i.e. 10 s on/10 s off) and an increase in gas sparging rate is needed, indicating the importance of shear rate and gas sparging frequency. An alternative gas sparging regime was subsequently tested in which filtration was conducted without gas sparging, followed by membrane relaxation for a short period coupled with gas sparging, to create a pseudo dead-end filtration cycle. Fouling characterisation evidenced considerable cake fouling rates of 200–250 mbar h−1 within each filtration cycle. However, long term fouling transient analysis demonstrated low residual fouling resistance, suggesting the cake formed during filtration was almost completely reversible, despite operating at a flux of 15 L m−2 h−1, which was equivalent or higher than the critical flux of the suspension. It is therefore asserted that by operating filtration in the absence of shear, fouling is less dependent upon the preferential migration of the sub-micron particle fraction and is instead governed by the compressibility of the heterogeneous cake formed, which enables higher operational fluxes to be achieved. Comparison of energy demand for the three gas sparging regimes to the energy recovered from municipal wastewater AnMBR demonstrated that only by using dead-end filtration can energy neutral wastewater treatment be realised which is the ultimate ambition for the technology
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C.Giosuè, Q.L.Yub, M.L.Ruello, F.Tittarelli, H.J.H.Brouwers “Effect of pore structure on the performance of photocatalytic lightweight lime-based finishing mortar”, Construction and Building Materials, 171 (May), 2018, 232-242
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Abstract:
The present paper aims to evaluate the performance of photocatalytic lightweight indoor hydraulic lime-based finishing mortars, with Portland cement-based finishing mortar as a reference. Two different types of aggregates, expanded glass and expanded silicate, are utilized to achieve the lightweight character and their contributions are investigated. The pore structure of the developed mortars is determined by mercury intrusion porosimetry (MIP) and BET methods. The mechanical strength, drying shrinkage, thermal physical properties and air pollutant removal ability of the mortars are investigated and the effects of pore structure on these properties are evaluated.
Due to the higher porosity, lime-based finishing mortars possess a higher capillary water absorption and higher drying shrinkage, which can be explained by the Kelvin-Laplace mechanism. The lime-based mortar shows very good thermal properties, with a thermal conductivity of 0.15 W/(m·K). The lime-based mortar shows a better ability of removing air pollutants, up to 46% under indoor air conditions laboratory test, compared to the cement-based mortar, which is attributed to the lower content of gel pores present in the lime-based mortar. Expanded glass shows positive influences concerning thermal properties and air pollutant removal ability compared to expanded silicate.
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M.PETITTA, L. MASTRORILLO,E. PREZIOSI,F. BANZATO,M.D. BARBERIO, A. BILLI, C. CAMBI, G. DE LUCA,G. DI CARLO, D. DI CURZIO, C. DI SALVO, T. NANNI, S. PALPACELLI, S. RUSI, M. SAROLI, M. TALLINI, A. TAZIOLI, D. VALIGI, P. VIVALDA and C. DOGLIONI, “Water-table and dischargechangesassociated with the 2016–2017 seismicsequence in central Italy: hydrogeological data and a conceptual model for fractured carbonate aquifers”, Hydrogeology Journal, 26(4) (June), 2018, 1009-1026
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Abstract:
A seismic sequence in central Italy from August 2016 to January 2017 affected groundwater dynamics in fractured carbonate aquifers. Changes in spring discharge, water-table position, and streamflowwere recorded for several months following nine Mw 5.0–6.5 seismic events. Data from 22 measurement sites, located within 100 km of the epicentral zones, were analyzed. The intensity of the induced changes were correlated with seismic magnitude and distance to epicenters. The additional post-seismic discharge from rivers and springs was found to be higher than 9 m3/s, totaling more than 0.1 km3 of groundwater release over 6 months. This huge and unexpected contribution increased streamflow in narrow mountainous valleys to previously unmeasured peak values. Analogously to the L’Aquila 2009 post-earthquake phenomenon, these hydrogeological changes might reflect an increase of bulk hydraulic conductivity at the aquifer scale, which would increase hydraulic heads in the discharge zones and lower them in some recharge areas. The observed changes may also be partly due to other mechanisms, such as shaking and/or squeezing effects related to intense subsidence in the core of the affected area, where effects had maximum extent, or breaching of hydraulic barriers.
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M. DEIANA, F. CERVI, M. PENNISI, M. MUSSI, C. BERTRAND, A. TAZIOLI, A. CORSINI, F. RONCHETTI, “Chemical and isotopic investigations (δ18O, δ2H, 3H, 87Sr/86Sr) to define groundwater processes occurring in a deep-seated landslide in flysch”, Hydrogeology Journal, https://doi.org/10.1007/s10040-018-1807-1
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Abstract:
Deep-seated landslides are complex systems. In many cases, multidisciplinary studies are necessary to unravel the key hydrological features that can influence their evolution in space and time. The deep-seated Berceto landslide, in the northern Apennines of Italy, has been investigated in order to define the origin and geochemical evolution of groundwater (GW), to identify the slope system hydrological boundary, and to highlight the GW flow paths, transit time and transfer modalities inside the landslide body. This research is based on a multidisciplinary approach that involves monitoring GW levels, obtaining analyses of water chemistry and stable and unstable isotopes (δ18O-δ2H, 3H, 87Sr/86Sr), performing soil leaching tests, geochemical modelling (PHREEQC), and principal component analysis (PCA). The results of δ18O-δ2H and 87Sr/86Sr analyses show that the source of GW recharge in the Berceto landslide is local rainwater, and external contributions from a local stream can be excluded. In the landslide body, two GW hydrotypes (Ca-HCO3 and Na-HCO3) are identified, and the results of PHREEQC and PCA confirm that the chemical features of the GW depend on water–rock interaction processes occurring inside the landslide. The 3H content suggests a recent origin for GW and appears to highlight mixing between shallow and deep GW aliquots. The 3H content and GW levels data confirm that shallow GW is mainly controlled by a mass transfer mechanism. The 3H analyses with GW levels also indicate that only deep GW is controlled by a pressure transfer mechanism, and this mechanism is likely the main influence on the landslide kinematics.
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A. Mazzoli, V. Corinaldesi, J. Donnini, C. Di Perna, D. Micheli, A. Vricella, R. Pastore, L. Bastianelli, F. Moglie, V. MarianiPrimiani, “Effect of graphene oxide and metallic fibers on the electromagnetic shielding effect of engineered cementitious composites”, Journal of Building Engineering, 18 (July), 2018, 33-39.
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Abstract:
Electromagnetic shielding and propagation in concrete structures are getting more and more interest in radiationhazard problems and wireless communications. The protection of sensitive environment is nowadays carried outby appropriate shielding room made of metallic walls. Their efficacy is counteracted by their heaviness, notadequate for the installation over existing building walls. The using of concrete composites filled by conductiveelements represents a valid alternative to metallic shielded room since they can be adopted to directly build upthe building walls and/or to easily plaster existing walls. Graphene oxide powder and metallic fibers are beingcurrently investigated as fillers in the manufacturing of electromagnetic shielding cementitious composites. Thenovelty of the present work is the characterization of a multi-reinforced cement realized by combining such twofiller typologies: the synergistic effects of graphene oxide microparticles and short steel fibers result in enhancementof both mechanical properties and EMI effectiveness of the cementitious composites.
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J. Donnini, G. Lancioni, V. Corinaldesi, “Failure modes in FRCM systems with dry and pre-impregnated carbon yarns: Experiments and modeling”, Composites Part B: Engineering, 140 (May), 2018, 57-67
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Abstract:
Fiber Reinforced Cementitious Matrix (FRCM) systems have emerged in recent years as an effective tool for strengthening and retrofitting of the existing built heritage. The effectiveness of FRCM systems is strongly related to the bond developed at the interface between inorganic matrix and fabric reinforcement and between the inorganic matrix and the substrate. However, since the major weakness is often located at the matrix-to-fiber interface, the study of stress-transfer mechanisms between fibers and matrix, and a better understanding of the failure processes become of fundamental importance. In this paper, interface bond-slip relations are derived from pull out tests on multifilament carbon yarns embedded in a cementitious matrix. Two different types of yarns are investigated, dry and pre-impregnated with epoxy resin. A variational model able to reproduce the mechanisms of interface debonding and frictional slippage observed in experiments is developed, where the constitutive parameters are calibrated on the base of the experimental data available from pull out tests. The model is implemented in a finite elements code, and pull out and double shear bond tests on masonry substrates are simulated. Finally, numerical results are compared with experimental evidences.
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G. Lancioni, V. Corinaldesi, “Variational modelling of diffused and localized damage with applications to fiber-reinforced concretes”, Meccanica, 53(3), 2018, 531-551
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Abstract:
A variational model for the evolution of damage in elastic materials is proposed, which is based on incremental energy minimization. Analytical solutions are determined in the one-dimensional case of a tensile bar, and the issue of their stability is addressed. Analytical results have given insights into the properties that elastic and damage energies must have in order that specific evolution processes are captured, such as diffuse damaging, progressive damage localization or brutal failure. Accordingly, expressions of elastic and damage energies are proposed aimed at reproducing the evolution of damage observed in high-performance fiber-reinforced concretes, which typically exhibit initial micro-cracking and subsequent macro-crack opening. Tensile tests on bone-shaped samples and three-points bending tests are reproduced, by implementing the model in a finite element code, and numerical results are compared with experimental evidences.
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